A common problem with vascular grafts is bleeding through holes punctured through the wall of a graft by suture needles or dialysis needles. Commercially available vascular grafts are most conventionally made of polyethylene terephthalate fabric or porous polytetrafluoroethylene tubing but materials of biologic origin such as human or bovine arteries or veins have also been used. Suture needles used to create an anastomosis with these vascular grafts typically result in significant bleeding through the resulting holes that must be stopped prior to closure of the operative incision. Dialysis treatment of individuals suffering from renal failure requires that the blood of the individual be withdrawn, cycled through a dialysis machine and returned to the individual. A common approach to providing the necessary hemodialysis access is the use of an implanted arteriovenous vascular graft that may be subcutaneously cannulated by a dialysis needle connected to a dialysis machine via lengths of tubing. These dialysis needles may also produce undesirable bleeding at the puncture site upon their removal.
Vascular grafts presently used for hemodialysis access are typically implanted for about 14 days prior to cannulation with a dialysis needle so that the graft has had time to become surrounded by fibrotic tissue and thereby reduce the risk of hemorrhage about the outer surface of the graft following removal of the dialysis needle. A vascular graft for dialysis applications that allows early cannulation following implantation without compromising other positive characteristics would be a significant step forward in the field of hemodialysis access.
Suture line bleeding resulting from graft penetration by a suture needle is frequently aggravated by tension applied to the sutures during construction of the anastomosis, the tension generally resulting in elongation and enlargement of the hole created by the penetration of the suture needle. Bleeding through suture holes must be stemmed before the access incision can be closed. Suture hole bleeding is thus responsible for both increased blood loss and increased time of operation. A vascular graft offering reduced suture bleeding would be of value in both regards.
An arteriovenous access vascular graft is described by U.S. Pat. No. 4,619,641 to Schanzer, which teaches the construction of an access graft comprising two commercially available expanded polytetrafluoroethylene (ePTFE) tubular vascular grafts in coaxial relationship with a space of about 1 mm disposed between the inner and outer grafts. The space is filled with an elastomer such as silicone. While this construction may offer reduced bleeding after withdrawal of a dialysis needle, the graft is stiff and consequently difficult to work with during implantation. A similar construction is described by U.S. Pat. No. 6,719,783 to Lentz et al., expressly teaching that the inner and outer ePTFE grafts are of dissimilar porosity.
Della Corna et al., in U.S. Pat. No. 4,955,899, teach the manufacture of an ePTFE tubular graft having a coating of an elastomer. The graft is made by longitudinally compressing an ePTFE tube on a mandrel, and coating the compressed tube with the elastomer. After removal from the mandrel, the resulting graft has some degree of longitudinal compliance. However, providing an exposed outer surface of elastomer is generally deemed undesirable.
House et al., in U.S. Pat. No. 4,877,661, teach an ePTFE graft that offers longitudinal compliance without requiring an elastomer. This graft is made by placing an ePTFE tube on a mandrel and compressing it longitudinally, and subsequently exposing it to heat. The resulting ePTFE tube has bent fibrils (from the longitudinal compression and heat-setting) that act as hairpin springs, allowing for good bending properties with kink resistance and longitudinal compliance. While this graft is effective as a dialysis graft that bleeds less than a conventional ePTFE graft following the removal of a needle, even less bleeding would be desirable.
Sowinski et al., US 2004/0024442, teach an ePTFE tubular graft wherein an ePTFE tube is coated with an interpenetrating elastomer and compressed longitudinally. It is further taught that the coating and compression steps are interchangeable. A similar process and tube is taught by Tu et al., EP 0256748. U.S. Pat. No. 5,529,820 to Nomi et al. teaches an ePTFE tube provided with an interpenetrating coating of an elastomer on one surface, for use as an endoscope tube.
U.S. Pat. No. 5,061,276 to Tu et al. describes a vascular graft comprising a composite tube of ePTFE and an elastomer, having an outer layer of elastomeric polymer fibers wound under tension about the circumference of the graft to cause retraction of the tubing from its original size. The wrapping of elastomeric fibers is provided with the intention of making the graft more compliant.
Myers et al., U.S. Pat. No. 5,628,782, teach an ePTFE vascular graft for dialysis that provides a layer of fibers about the outer surface of an ePTFE tubular graft. The fibers are preferably provided with an outer covering of ePTFE film to retain the fibers to the graft surface. The presence of the fibers provides a large surface area to any blood escaping a puncture site, encouraging hemostasis. The fibers result in a somewhat bulky graft with poorer graft handling properties than many conventional vascular grafts. Another ePTFE vascular graft for dialysis is taught by Silverman et al. in U.S. Pat. No. 5,931,865. A multiple layer tubular construction is described, wherein one layer is under longitudinal compression relative to another layer.
Not withstanding the advantages of the above described devices, there remains a need for vascular grafts and other implantable devices that offer improved handling properties to the surgeon and further reduced leakage of body fluids such as blood following puncture by a suture needle or a dialysis needle.